This invention relates to an apparatus for controlling the throttle valve of the engine of an automotive vehicle, the term "automotive vehicle" being used herein to include passenger vehicles, trucks, tractors, and other vehicles which are powered by an internal combustion engine.
Up to the present time, the mechanism for opening and closing the throttle valve of an automotive engine was generally a mechanical linkage connected between the throttle valve and the accelerator pedal of the vehicle. In recent years, however, a throttle valve control mechanism has been developed which opens and closes the throttle valve using an electronically-controlled actuator. The actuator includes an electric drive motor which rotates the throttle valve in response to electric signals from a controller. The controller calculates the optimal degree of throttle opening based on the amount by which the accelerator pedal is depressed by the driver, on the operational state of the engine (indicated, for example, by the engine rotational speed), and on the running condition of the vehicle (indicated, for example, by the speed of the vehicle or by which gears are engaged). The controller then outputs suitable electrical control signals to the actuator. As there is no mechanical linkage between the throttle valve and the accelerator pedal, play and frictional losses which are inherent drawbacks of a mechanical linkage are avoided.
However, if the electronically-controlled actuator of such a throttle valve control mechanism becomes inoperable, depressing the accelerator pedal has no effect on the throttle valve. Therefore, a vehicle which has this type of throttle valve control mechanism must be equipped with a safety device which prevents the vehicle from running with the throttle stuck in an open position should the actuator become inoperable. Usually, this safety device is one which closes the throttle valve when the actuator malfunctions. Japanese Patent Application Laid-Open No. 55-145867 (1980) discloses a number of such safety devices. One which is disclosed therein is a safety device comprising a return spring which is mounted on the shaft of a throttle valve and closes the throttle valve when the control apparatus for the throttle valve malfunctions. Another is a safety device comprising an electromagnetic clutch which disconnects an electronically-controlled actuator from the shaft of the throttle valve when the throttle valve control apparatus malfunctions. A third safety device comprises a return spring and an electromagnetic clutch, the return spring being released so as to close the throttle valve when the electromagnetic clutch is released.
However, as these safety devices close the throttle valve when the actuator malfunctions, the vehicle becomes unable to move under its own power. Therefore, when the throttle valve control apparatus malfunctions, the vehicle must be towed by another vehicle to a garage and be repaired.